Immunohistochemical Detection of hTERT Protein in Soft Tissue Sarcomas

The role of telomeres in musculoskeletal diseases

The telomeric region of repetitive DNA sequences at the end of chromosomes prevents end-to-end fusion of chromosome terminals and deterioration of the doublestrand free ends. Because of the 'end-replication problem', telomeres shorten with each round of cell division, resulting in cell senescence. The enzyme telomerase compensates for telomere shortening by elongating telomeric sequences, thereby prolonging the lifespan of the cell. Studies of articular cartilage and bone tissues have indicated that telomere shortening limits normal cell function and proliferation, while the telomere maintenance mechanisms of osteosarcoma cells facilitate escape from cell death and promote immortality. This article reviews the literature on this topic and provides an extensive discussion of the basic molecular biology and roles of telomeres and telomerase in musculoskeletal diseases such as osteoarthritis, osteoporosis and osteosarcoma. Findings to date suggest that telomeres and telomerase may become novel therapeutic targets for the diagnosis, treatment and prevention of musculoskeletal disorders.

Correlation between p38 mitogen-activated protein kinase and human telomerase reverse transcriptase in sarcomas

Background

One of the major components of telomerase is the human telomerase reverse transcriptase (hTERT) as the catalytic protein. hTERT mRNA expression are reported to be associated with prognosis and tumor progression in several sarcomas. However, there is no clear understanding of the mechanisms of hTERT in human sarcomas. Recent studies have suggested that signals transmitted through p38 mitogen-activated protein kinase (MAPK) can increase or decrease hTERT transcription in human cells. The purpose of this study was to analyse the correlation between p38 MAPK and hTERT in sarcoma samples.

Methods

We investigated 36 soft tissue malignant fibrous histiocytomas (MFH), 24 liposarcomas (LS) and 9 bone MFH samples for hTERT and p38 MAPK expression. Quantitative detection of hTERT and p38 MAPK was performed by RT-PCR.

Results

There was a significant positive correlation between the values of hTERT and p38 MAPK in all samples (r = 0.445, p = 0.0001), soft tissue MFH (r = 0.352, p = 0.0352), LS (r = 0.704, p = 0.0001) and bone MFH samples (r = 0.802, p = 0.0093). Patients who had a higher than average expression of p38 MAPK had a significantly worse prognosis than other patients (p = 0.0036).

Conclusions

p38 MAPK may play a role in up-regulation of hTERT, and therefore, p38 MAPK may be a useful marker in the assessment of hTERT and patients' prognosis in sarcomas.

Immunohistochemistry for human telomerase reverse transcriptase catalytic subunit (hTERT): a study of 143 benign and malignant soft tissue and bone tumours

AIMS

Only a small number of mesenchymal tumours have been previously evaluated for hTERT expression. We hypothesised that hTERT expression would be frequently present in sarcomas, but not in benign tumours.

METHODS

Sections from 143 bone/soft tissue tumours were immunostained for hTERT (44F12, 1:20; Novocastra) using steam heat-induced epitope retrieval and the Dako Envision system. Normal lymphocytes served as positive internal controls. Positive cases showed 'speckled' nuclear/nucleolar staining in >10% of cells, in accordance with previous studies. Fisher's exact test was used for statistical analysis. The result was checked against the G test and Chi-squared test with Yates correction, and was concordant.

RESULTS

hTERT expression was seen in nine of 71 (13%) benign and 33 of 72 (46%) malignant tumours (p > or = 0.001). hTERT was positive in >50% of osteosarcomas, malignant peripheral nerve sheath tumours, liposarcomas, and angiosarcomas. All positive sarcomas were high grade (FNCLCC grade II or III). Among benign tumours, only schwannomas and chondromas were positive in >30% of cases. Positive normal tissues included lymphocytes, multinucleated histiocytes, keratinocytes, adnexal glands, hepatocytes and basal cells of respiratory mucosa.

CONCLUSIONS

hTERT expression is significantly more common in sarcomas as compared with benign tumours. Restriction of hTERT expression to high grade lesions, and its absence in low grade sarcomas (including the well-differentiated component of dedifferentiated liposarcoma), suggests that telomerase activation is a late event in sarcoma progression. Importantly, however, hTERT can be expressed in some benign tumours, notably schwannoma and chondroma, and it is doubtful that hTERT expression alone will allow the discrimination of benign from malignant soft tissue/bone tumours. Importantly, hTERT expression is often only focal and its identification may require careful evaluation of an entire section, suggesting that this technique is best applied to whole sections, rather than tissue microarrays.

Distribution and prognostic significance of human telomerase reverse transcriptase (hTERT) expression in giant-cell tumor of bone

Giant-cell tumor of bone is considered a benign, locally aggressive and rarely metastasizing neoplasm of bone. Specific microscopic or radiographic findings that reliably predict behavior have remained elusive. However, recent evidence suggests that activity of the telomerase enzyme complex correlates with recurrence in giant-cell tumor, although the subset of cells with telomerase activity in these heterogeneous tumors has not been defined. In the present study, we investigated whether immunostaining for human telomerase reverse transcriptase, a component of the telomerase complex, correlates with outcome in giant-cell tumor and the distribution of telomerase reverse transcriptase staining in these tumors. We analyzed 58 cases of giant-cell tumor for the presence and pattern of telomerase reverse transcriptase immunostaining, presence of soft tissue involvement and the type of initial surgery, and correlated these findings with recurrence-free survival and metastasis-free survival. Specific staining with telomerase reverse transcriptase was present in 20 out of 58 tumors (35%) in the nuclei of mononuclear cells and, occasionally, osteoclast-like giant cells. Furthermore, positive telomerase reverse transcriptase immunohistochemistry correlated with recurrence-free survival (P=0.02), whereas the presence of soft tissue extension (P=0.3) and the type of initial surgery (P=0.2) did not. Only soft-tissue extension significantly correlated with metastasis-free survival (P=0.003). Therefore, telomerase reverse transcriptase expression may predict recurrence in giant-cell tumor insofar as positive immunostaining correlates with shorter recurrence-free survival and may be a useful prognostic marker to stratify patients to more aggressive treatment protocols.

Telomere maintenance in sarcomas

PURPOSE OF REVIEW

To examine the activation of telomere maintenance in a variety of sarcoma subtypes, and to review the consequences of telomere maintenance with respect to genome stability and tumor progression.

RECENT FINDINGS

A hallmark of tumor cells is replicative immortality, which can be achieved, in part, by the activation of a telomere maintenance mechanism. A significant proportion of tumors show activation of telomerase, a specialized enzyme that adds telomeric repeats to pre-existing telomeres. Recent work has demonstrated, however, that a telomerase-independent mechanism called ALT (alternative lengthening of telomeres) is activated as frequently as telomerase in a variety of tumor types, particularly those of mesenchymal origin. Accordingly, panels of mesenchymal tumors have been interrogated for telomere maintenance mechanism, as well as characteristics such as tumor grade and patient survival.

SUMMARY

These studies indicate a strong positive correlation between the activation of a telomere maintenance mechanism and tumor progression in sarcomas. In addition, the activation of either ALT or telomerase is correlated with poorer patient prognosis as compared with a lack of telomere maintenance. Ongoing studies aimed at elucidating the roles of ALT and telomerase in tumorigenesis should ultimately allow for the development of strategies to improve treatment of these malignancies.